The UK guidelines were drawn up in 1994, after several national surveys found low levels of activity were contributing to poor health.

'Smaller bouts'

But there's an inherent tension in giving public health advice.

Broad advice can be sold in a single message, but nuance is harder to convey.

Image caption
Dr Michael Mosley finds out why doing the same amount of exercise might not work for everyone

Stuart Biddle, professor of physical activity at Loughborough University helped to write the UK guidelines.

He says: "The debate was really around not so much whether the science showed physical activity was good for health, but to come up with sensible and evidence-based guidelines such as how much exercise, how often should we do it, can we break it up into smaller bouts, and it's really that which was probably the most contentious."

"During this year we've learned that while regular exercise will reduce your chance of developing or progressing to Type 2 diabetes, it was always expected that would also benefit your cardiovascular system," he said.

People who report that they do more physical activity seem to be better off.Stuart Biddle, Professor of physical activity at Loughborough University

Carol Garber, a vice-president of the American College of Sports Medicine, says guidelines could be better understood.

"Part of it is that they are complicated, the other is that we've not done a very good job of getting the information out to people in a way that it's easy to understand and that they can take and implement it in their daily lives."

The UK guidelines have now been updated to include specific advice for age-groups, strength training and avoiding sedentary behaviour - the "silent killer" of sitting in a chair for several hours each day.

The Department of Health says "Being active can help protect against heart disease, Type 2 diabetes and certain types of cancer which is why we have guidance on physical activity tailored to each age group."

I was surprised by just how few people, other than the experts, knew what the activity guidelines are.

The message to be active is broadly understood, but the other crucial thing - to get up and move around as often as possible - is largely ignored.

Based on what I've learnt I've been trying out my own 'Twenty Plus' campaign; 20 seconds of intense activity when I can (running up stairs, cycling like crazy for short bursts on my bike), a minimum of 20 minutes of walking every day, and no more than 20 minutes of sitting at my computer or in front of the telly without getting up and moving around.

So far it's been very manageable.

You can listen to Michael Mosley on BBC Radio 4's You & Yours on 2 January at 12:00.